The invention relates to a method for redundant anode sputtering with a dual anode arrangement. According to this method, two anodes are operated alternately opposite each other as the anode of the plasma discharge and as the cathode for self-cleaning during the etching phase, and the cathode of the plasma discharge is recurrently reversed in polarity for a short period of time, in order to reduce the static charge.
The invention also relates to an arrangement that is intended for redundant anode sputtering with a dual anode arrangement and that comprises a vacuum chamber with a chamber wall, and therein arranged are also a cathode and a first and a second anode which [is supplied with voltage] by means of an H bridge circuit, which comprises a first bridge branch and a second bridge branch. In this case both bridge branches form together on the one side a plus connection, and on the other side both bridge branches form together a minus connection.
In a sputtering system a gas discharge is ignited between a cathode and an anode at a pressure of a few μbar. The material of the target, which forms the surface of the cathode that is exposed to the gas discharge, is stripped by an intensive ion bombardment. The cathode sputtering process generates a cloud of material vapor, which settles on all of the parts in the vacuum chamber. The aim of the design of sputtering systems is to collect on the substrate as much as possible of this material that has sputtered off and to allow as little as possible to land on the anodes. Since the deposition phase often produces, intentionally or unintentionally, poorly conducting or insulating materials, the current flow through the layered anode surface is significantly impeded with time so that the stability of the gas discharge is disturbed until totally quenched.
Long term stable processes, in which oxides or nitrides are deposited from a ceramic target at high sputtering rates, are a challenge for the design of a sputtering system.
The use of two anodes, which are operated alternately as the anode and as the cathode for self-cleaning, has already been known since the U.S. Pat. No. 6,183,605. The arrangement implements a redundant anode sputtering—that is, a cathode sputtering—with an additional anode. The drawback with this solution is the absence of means to control the etching effect in the presence of cathodically connected anodes.
The PCT application WO2007/051461 describes a control process for the etching effect. The document comprises two embodiments, with a medium frequency generator or with a DC power supply (direct voltage power supply), which divides in a pulsed manner the power between the cathode and the two anodes. In this case one of the solutions with a DC power supply provides a classical H bridge circuit comprising four switches, in particular comprising insulated gate bipolar transistors (IGBT), which effect, on the one hand, a polarity reversal of the anodes (electrodes) and, on the other hand, a short-term polarity reversal of the cathode, in order to extract the electrons from the remaining plasma and for discharging. This solution and its voltage behaviors are reproduced in FIG. 1 and FIG. 2.
In this case the commercially available DC power supplies with the principle of redundant anode sputtering are operated with two anodes (dual anodes). As a result, however, it is necessary to use switches, which effect the controlled changeover of the currents to the anodes, but are protected against the loading by the DC power supplies.
The U.S. Pat. No. 5,427,669 discloses a pulsed direct current power supply (pulsed power supply), which reverses the polarity of the cathode for a short period of time so that any charge to the cathode is discharged. Owing to the high du/dt values (voltage gradient) the short-term polarity reversal of the cathode generates in the circuit a dangerous load for the semiconductor switches, which are generally used in jumpers. In this case the term “short-term” means that the duration of the changeover pulse is less than the time until a next changeover pulse—thus, the time, in which the cathode voltage is negative.
In addition, this circuit is provided for a redundant anode sputtering, but not for use with dual anodes.
An additional risk, in particular for semiconductor components as switches, is the sudden quenching of the plasma as a result of, for example, too low pressure. This situation, which is called load shedding, produces extreme overvoltages, which lead to the destruction of semiconductor components, if it is not possible to limit the voltages.